Laser-releasable bonding materials for 3-d ic applications

ABSTRACT

Novel polyketanil-based compositions for use as a laser-releasable composition for temporary bonding and laser debonding processes are provided. The inventive compositions can be debonded using various UV lasers, at wavelengths from about 300 nm to about 360 nm, leaving behind little to no debris. The layers formed from these compositions possess good thermal stabilities and are resistant to common solvents used in semiconductor processing. The compositions can also be used as build-up layers for redistribution layer formation.

RELATED APPLICATIONS

The present application is a divisional of pending U.S. patentapplication Ser. No. 16/747,271, filed Jan. 20, 2020, entitledLASER-RELEASABLE BONDING MATERIALS FOR 3-D IC APPLICATIONS, incorporatedby reference in its entirety herein. U.S. patent application Ser. No.16/747,271 claims the priority benefit of U.S. Provisional PatentApplication Ser. No. 62/795,092, filed Jan. 22, 2019, entitledLASER-RELEASABLE BONDING MATERIALS FOR 3-D IC APPLICATIONS, incorporatedby reference in its entirety herein.

BACKGROUND Field of the Invention

The present invention relates to laser-releasable compositions for usein temporary wafer bonding processes or for use as a build-up layer induring redistribution layer formation.

DESCRIPTION OF RELATED ART

Temporary wafer bonding (“TWB”) normally refers to a process forattaching a device wafer or microelectronic substrate to a carrier waferor substrate by means of a polymeric bonding material. After bonding,the device wafer may be thinned typically to less than 50 μm and/orprocessed to create through-silicon vias (“TSV”), redistribution layers,bond pads, and other circuit features on its backside. The carrier wafersupports the fragile device wafer during the backside processing, whichcan entail repeated cycling between ambient temperatures and hightemperatures (>250° C.), mechanical shocks from wafer handling andtransfer steps, and strong mechanical forces, such as those imposedduring wafer back-grinding processes used to thin the device wafer. Whenall of this processing has been completed, the device wafer is usuallyattached to a film frame and then separated (i.e., debonded) from thecarrier wafer and cleaned before further operations take place.

Most TWB processes use either one or two layers between the devicesubstrate and the carrier substrate. Depending on the TWB process, thedevice and carrier substrate can be separated by a variety of separationmethods, such as chemical debonding, thermal slide debonding, mechanicaldebonding, or laser debonding, with the latter becoming a preferreddebonding method. In the case of a one-layer, laser debond system, thebonding layer responds to radiation from a laser or other light source,which leads to decomposition of the layer itself, causing bondingintegrity to be lost within the structure and allowing it to come apartwithout applying mechanical force. In the case of a two-layer laserdebond system, a second polymeric bonding material layer is utilized,typically adjacent to the device surface. The second layer is easilycleaned from the device wafer surface after the post-processingdestruction of the laser-sensitive layer and separation of the bondedwafer pair.

Laser-induced release materials are available for operating at laserwavelengths ranging from ultraviolet (e.g., 248 nm, 308 nm and 355 nm)to near infrared (e.g., 1064 nm) wavelengths.

Laser release technology provides high throughput and low stress duringthe release process, effective thin-substrate handling, and ease ofapplication, even with large panels. Laser release technology that canbe utilized in different applications in packaging areas such astemporary bonding, fan-out wafer-level packaging, lamination, 2.5D/3Dintegration using through-silicon vias (TSVs), system-in-packaging(“SiP”), package-on-package (“PoP”), and other heterogeneous integrationinfrastructures is needed. This technology requires laser releasematerials that have high sensitivity, thus allowing for lower energyapplication, shorter debond times, and less debris after debonding.

SUMMARY OF THE INVENTION

The present invention broadly comprises a temporary bonding methodcomprising providing a stack comprising:

a first substrate having a back surface and a front surface;

a bonding layer adjacent the front surface;

a second substrate having a first surface; and

a release layer between the first surface and the bonding layer, withthe release layer comprising a polyketanil. The release layer is exposedto laser energy so as to facilitate separation of the first and secondsubstrates.

The invention also provides a microelectronic structure comprising:

a first substrate having a back surface and a front surface;

a bonding layer adjacent the front surface;

a second substrate having a first surface; and

a release layer between the first surface and the bonding layer, withthe release layer comprising a polyketanil.

In another embodiment, the invention also provides a method of forming arelease layer.

The method comprises applying a composition to a substrate surfacecomprising glass or other transparent material. The compositioncomprises a polyketanil dissolved or dispersed in a solvent system. Thecomposition is heated at a temperature of from about 60° C. to about350° C. to form the release layer.

In a further embodiment, the inventive method comprises forming abuild-up layer on the surface of a substrate. The build-up layercomprises a polyketanil and has an upper surface that is remote from thesurface of the substrate. A first redistribution layer is formed on theupper surface and optionally one or more additional redistributionlayers is formed on the first redistribution layer.

In yet a further embodiment, a microelectronic structure comprises asubstrate having a surface. A build-up layer is on the substratesurface, and the build-up layer comprises a polyketanil and has an uppersurface that is remote from the substrate surface. There is a firstredistribution layer on the upper surface.

Another embodiment of the invention provides a polymer comprisingrecurring monomers of

where each of R₁ to R₄:

-   -   can be the same or different; and    -   is individually selected from the group consisting of hydrogen,        alkyls, alkoxys, hydroxyls, and polyethylene glycol chains.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a schematic drawing of a temporarybonding process according to one embodiment of the invention;

FIG. 2 is a schematic drawing illustrating redistribution layerformation according to another embodiment of the invention; and

FIG. 3 is a graph showing the spectra of n and k values as determined inExample 3.

DETAILED DESCRIPTION

The present invention is concerned with novel laser-releasablecompositions or build-up compositions as well as methods of using thosecompositions.

Laser-Releasable or Build-Up Polymers and Compositions 1. Polyketanils

The compositions for use in the present invention comprise polyketanils,which are sometimes referred to as polyketimines. A ketanil bond is onethat forms between a ketone group and amine group. This bond preferablycomprises a carbon atom double-bonded to a nitrogen atom. The carbonatom that is part of the double bond is preferably bonded to two othercarbon atoms (one or both of which is preferably part of an aromaticstructure), while the nitrogen atom that is part of the double bond ispreferably bonded to another carbon atom, with that other carbon atombeing part of an aromatic structure. The foregoing aromatic structuresare preferably phenyl groups. The ring members of the phenyl groups canbe unsubstituted or substituted (e.g., with —NH₂).

In one preferred embodiment, the polyketanil used in the presentinvention is polymerized from a monomer having an amine functional groupand a ketone functional group. The monomer also comprises an aromaticmoiety, and both the amine and ketone functional groups are bonded tothe aromatic moiety. A preferred structure for this monomer is:

where:

-   -   each of R₁ to R₄ can be the same or different; and    -   each of R₁ to R₄ is selected from the group consisting of        hydrogen, alkyls (preferably C₁-C₁₀ and more preferably C₁-C₆),        alkoxys (preferably C₁-C₁₀ and more preferably C₁-C₆),        hydroxyls, and polyethylene glycol chains (preferably C₁-C₁₀ and        more preferably C₁-C₆).

In some embodiments, it is preferred that one or more of R₁ to R₄ ishydrogen, as too many or very large substituents could create sterichindrance that could impede the polyketanil-forming reaction. Aparticularly preferred monomer according to the foregoing structure is4′-aminoacetophenone (i.e., each of R₁ to R₄ is hydrogen).

Preferred polyketanils for use in the present invention can be polymericor oligomeric, but when polymerized or oligomerized, the monomers shouldabsorb light at wavelengths of from about 100 nm to about 500 nm, morepreferably from about 300 nm to about 400 nm, thus imparting lightabsorbance properties onto the polyketanils. Advantageously, the iminestructure formed from the polyketanil structure produces moderate tohigh conjugation, giving strong laser absorption at UV wavelengths. Onepreferred polyketanil has the structure:

where:

-   -   each of R₁ to R₄ can be the same or different; and    -   each of R₁ to R₄ is selected from the group consisting of        hydrogen, alkyls (preferably C₁-C₁₀ and more preferably C₁-C₆),        alkoxys (preferably C₁-C₁₀ and more preferably C₁-C₆),        hydroxyls, and polyethylene glycol chains (preferably C₁-C₁₀ and        more preferably C₁-C₆).

Again, in the above polymerized structure, it is particularly preferredthat each of R₁ to R₄ is hydrogen.

The above polyketanils can be synthesized using a Schiff base reaction.As noted above, the polyketanil is generally formed by a reactionbetween an amine and a ketone to form a ketanil bond for the repeatingstructure of the polyketanil. The reaction is performed at hightemperatures, preferably in excess of about 180° C., in the presence ofan acid catalyst. Water should be removed from the reaction to push thereaction forward and decrease the ability of the reaction to reverse.

Suitable catalysts for use during polymerization include those selectedfrom the group consisting of sulfuric acid, p-toluenesulfonic acid(pTSA), hydrochloric acid, other strong acids, and mixtures of theforegoing. A weak acid with a high boiling point or a metal-based Lewisacid such as zinc chloride would also be suitable. The amount ofcatalyst present is typically from about 0.1% to about 5% by molarpercent, and preferably from about 0.5% to about 1.5% by molar percentcatalyst, based upon the number of moles of monomer.

Suitable solvents for use in the polymerization system include thoseselected from the group consisting of gamma butyrolactone (GBL),n-methyl-2-pyrrolidone (NMIP), dimethylacetamide (DMAc), dimethylsulfoxide (DMSO), benzyl alcohol, other high-boiling-point polarsolvents, and mixtures thereof. The solvent is typically present duringpolymerization at levels of from about 20% to about 80% by weight, andpreferably from about 30% to about 70% by weight solvent, based upon thetotal weight of all components in the reaction mixture taken as 100% byweight, with the solids being the remainder.

The polymerization reaction is carried out at a temperature of fromabout 150° C. to about 300° C., and more preferably from about 180° C.to about 200° C., for a time period of from about 12 hours to about 60hours, more preferably from about 24 hours to about 48 hours. Thewater/solvent mixture generated during the reaction is preferablyremoved to allow the reaction to proceed. The crude product ispreferably precipitated in an alcohol and dried under vacuum.

Regardless of how the polyketanil is formed, it preferably has a weightaverage molecular weight of from about 1,000 Daltons to about 100,000Daltons, preferably from about 1,500 Daltons to about 50,000 Daltons,even more preferably from about 2,000 Daltons to about 10,000 Daltons,as determined by GPC.

2. Polyketanil Compositions

The laser-releasable or build-up compositions for use in the inventionare formed by simply dissolving the polyketanil and any optionalingredients in a solvent system. Suitable solvents include thoseselected from the group consisting of ethyl lactate, cyclopentanone,cyclohexanone, propylene glycol methyl ether acetate (PGMEA), propyleneglycol methyl ether (PGME), GBL, benzyl alcohol, and mixtures thereof.Preferably, dissolution is allowed to take place over the course ofabout 24 hours, while stirring, resulting in a substantially homogeneoussolution. The solution is preferably filtered before use.

The final laser-releasable or build-up compositions preferably comprisefrom about 1% to about 40% by weight solids, more preferably from about3% to about 25% by weight solids, and even more preferably from about 5%to about 20% by weight solids, based upon the total weight of thecomposition taken as 100% by weight. These solids are usually about 100%by weight polyketanil, however, in some instances, the solids may befrom about 20% to about 100% by weight polyketanil, preferably fromabout 50% to about 100% by weight polyketanil, and more preferably fromabout 75% to about 100% by weight polyketanil, based upon the totalweight of solids in the composition taken as 100% by weight.

In one embodiment, no other ingredients are included in the compositionbesides the polyketanil and solvent system. That is, the compositionconsists essentially of, or even consists of, the polyketanil in thesolvent system.

In another embodiment, the composition comprises a polyketanil and apolymer (or more than one polymer) that is not a polyketanil dispersedor dissolved in a solvent system (such as the solvents notedpreviously). In this embodiment, the solids and solvent levels are asdescribed previously, but the composition comprises:

-   -   from 0.1% to about 99.9% by weight polyketanil, more preferably        from about 10% to about 90% by weight polyketanil, and even more        preferably from about 25% to about 75% by weight polyketanil,        based upon the total weight of the solids in composition taken        as 100% by weight; and    -   from 0.1% to about 99.9% by weight polymer(s) other than        polyketanil, more preferably from about 10% to about 90% by        weight polymer(s) other than polyketanil, and even more        preferably from about 25% to about 75% by weight polymer(s)        other than polyketanil, based upon the total weight of the        solids in composition taken as 100% by weight.

In another embodiment, a polyketanil composition as described herein canbe blended with a commercially available composition to adjust theproperties of that commercially available composition. For example, acommercially available composition that does not have sufficientabsorbance at the user's target wavelength (e.g., about 300 nm to about400 nm) can be blended with a polyketanil composition to increase thatcommercial composition's absorbance at that wavelength. In thisinstance, the respective quantities of the solids, solvent, polyketanil,and polymer(s) other than polyketanil will be the same as described inthe preceding paragraph.

In one embodiment, the composition is essentially free of crosslinkingagents. That is, the composition comprises less than about 3% by weight,preferably less than about 1% by weight, and even more preferably about0% by weight crosslinking agent, based upon the total weight of thecomposition taken as 100% by weight. In this embodiment, the polyketanilcan be the only polymer or one of a polymer blend, as described above,and at the quantities described previously.

In another embodiment, the composition includes a crosslinking agent.That is, the composition comprises from about 0.1% to about 20% byweight crosslinking agent, more preferably from about 0.5% to about 10%by weight crosslinking agent, and even more preferably from about 1% toabout 5% by weight crosslinking agent, based upon the total weight ofthe polyketanil and any other polymers taken as 100% by weight. In thisembodiment, the polyketanil can be the only polymer or one of a polymerblend, as described above, and at the quantities described previously.

In another embodiment, the composition includes one or more encappingagents. The encapping agents contain functional groups that can reactwith the amine functional group or the ketone functional group of themonomer to slow or stop the polymerization reaction. Suitable endcappersinclude cyclic anhydrides (such as maleic anhydride, phthalic anhydride,and naphthalic anhydride), monofunctional aldehydes (such asbenzaldehyde, trans-2-pentenal, and cinnamaldehyde), monofunctionalketones (such as acetophenone, raspberry ketone, and 2-acetylthiophene),monofunctional primary amines (such as aniline, p-anisidine and3-amino-4-methylphenol), and monofunctional carboxylic acids (such asbenzoic acid, p-toluic acid, and 1-naphthoic acid).

Regardless of the exact formulation, the composition can be used as alaser-releasable composition in a temporary bonding process totemporarily bond a device substrate to a carrier substrate using theprocesses described below. Additionally, the laser-releasablecomposition can be used as a build-up composition in a redistributionlayer formation process, as also described below.

Methods of Using Laser Releasable or Build-Up Compositions 1. TemporaryBonding Embodiment

Referring to FIG. 1(a) (not to scale), a precursor structure 10 isdepicted in a schematic and cross-sectional view. Structure 10 includesa first substrate 12. Substrate 12 has a front or device surface 14, aback surface 16, and an outermost edge 18. Although substrate 12 can beof any shape, it would typically be circular in shape. Preferred firstsubstrates 12 include device wafers such as those whose device surfacescomprise arrays of devices (not shown) selected from the groupconsisting of integrated circuits, MEMS, microsensors, powersemiconductors, light-emitting diodes, photonic circuits, interposers,embedded passive devices, and other microdevices fabricated on or fromsilicon and other semiconducting materials such as silicon-germanium,gallium arsenide, gallium nitride, aluminum gallium arsenide, aluminumindium phosphide, and indium gallium phosphide. The surfaces of thesedevices commonly comprise structures (again, not shown) formed from oneor more of the following materials: silicon, polysilicon, silicondioxide, silicon (oxy)nitride, metals (e.g., copper, aluminum, gold,tungsten, tantalum), low k dielectrics, polymer dielectrics, and variousmetal nitrides and silicides. The device surface 14 can also include atleast one structure selected from the group consisting of: solder bumps;metal posts; metal pillars; and structures formed from a materialselected from the group consisting of silicon, polysilicon, silicondioxide, silicon (oxy)nitride, metal, low k dielectrics, polymerdielectrics, metal nitrides, and metal silicides.

A composition is applied to the first substrate 12 to form a bondinglayer 20 on the device surface 14, as shown in FIG. 1(a). Bonding layer20 has an upper surface 21 remote from first substrate 12, andpreferably, the bonding layer 20 is formed directly adjacent the devicesurface 14 (i.e., without any intermediate layers between the bondinglayer 20 and substrate 12). Although bonding layer 20 is shown to coverthe entire device surface 14 of first substrate 12, it will beappreciated that it could be present on only portions or “zones” ofdevice surface 14, as shown in U.S. Patent Publication No. 2009/0218560,incorporated by reference herein.

The bonding composition can be applied by any known application method,including dip coating, roller coating, slot coating, die coating, screenprinting, draw-down coating, or spray coating. Additionally, thecoatings may be formed into free-standing films before application tothe device substrate or carrier substrate surface. One preferred methodinvolves spin-coating the composition at speeds of from about 200 rpm toabout 5,000 rpm (preferably from about 500 rpm to about 3,000 rpm) for atime period of from about 5 seconds to about 120 seconds (preferablyfrom about 30 seconds to about 90 seconds).

After the composition is applied, it is preferably heated to atemperature of from about 50° C. to about 250° C., and more preferablyfrom about 80° C. to about 220° C. and for time periods of from about 60seconds to about 8 minutes (preferably from about 90 seconds to about 6minutes). Depending upon the composition used to form the bonding layer20, baking can also initiate a crosslinking reaction to cure the layer20. In some embodiments, it is preferable to subject the layer to amulti-stage bake process, depending upon the composition utilized. Also,in some instances, the above application and bake process can berepeated on a further aliquot of the composition, so that the firstbonding layer 20 is “built” on the first substrate 12 in multiple steps.The resulting bonding layer 20 should have an average thickness (averagetaken over five measurements) of from about 1 μm to about 200 μm, morepreferably from about 10 μm to about 150 μm, and even more preferablyfrom about 20 μm to about 120 μm.

The materials from which the bonding layer 20 is formed should becapable of forming a strong adhesive bond with the first substrate 12.Anything with an adhesion strength of greater than about 50 psig,preferably from about 80 psig to about 250 psig, and more preferablyfrom about 100 psig to about 150 psig, as determined by ASTMD4541/D7234, would be desirable for use as a bonding layer.

Advantageously, the compositions for use in forming the bonding layer 20can be selected from commercially available bonding compositions thatwould be capable of being formed into a layer possessing the aboveadhesive properties, while being removable by heat and/or solvent.Typical such compositions are organic and will comprise a polymer oroligomer dissolved or dispersed in a solvent system. The polymer oroligomer is typically selected from a group consisting of polymers andoligomers of cyclic olefins, epoxies, acrylics, silicones, styrenics,vinyl halides, vinyl esters, polyamides, polyimides, polysulfones,polyethersulfones, cyclic olefins, polyolefin rubbers, polyurethanes,ethylene-propylene rubbers, polyamide esters, polyimide esters,polyacetals, polyvinyl butyral, and mixtures of the foregoing. Typicalsolvent systems will depend upon the polymer or oligomer selection.Typical solids contents of the bonding compositions will range fromabout 1% to about 60% by weight, and preferably from about 3% by weightto about 40% by weight, based upon the total weight of the compositiontaken as 100% by weight. Some suitable compositions are described inU.S. Patent Publication Nos. 2007/0185310, 2008/0173970, 2009/0038750,and 2010/0112305, each incorporated herein by reference.

A second precursor structure 22 is also depicted in a schematic andcross-sectional view in FIG. 1(a). Second precursor structure 22includes a second substrate 24. In this embodiment, second substrate 24is a carrier wafer. That is, second substrate 24 has a front or carriersurface 26, a back surface 28, and an outermost edge 30. Although secondsubstrate 24 can be of any shape, it would typically be circular inshape and sized similarly to first substrate 12. Preferred secondsubstrates 24 include a clear wafer or any other transparent (to laserenergy) substrate that will allow the laser energy to pass through thecarrier substrate, including, but not limited to, glass, Corning Gorillaglass, and sapphire. One especially preferred glass carrier wafer is aCorning EAGLE XG glass wafer.

A polyketanil composition as described above is applied to the secondsubstrate 24 to form a laser release layer 32 on the carrier surface 26,as shown in FIG. 1(a). Alternatively, structure 22 can be providedalready formed. Release layer 32 has an upper surface 33 remote fromsecond substrate 24, and a lower surface 36 adjacent second substrate24. Preferably, the release layer 32 is formed directly adjacent thecarrier surface 26 (i.e., without any intermediate layers between thesecond bonding layer 32 and second substrate 24).

The laser-releasable composition can be applied by any known applicationmethod, with one preferred method being spin-coating the composition atspeeds of from about 500 rpm to about 3,000 rpm (preferably from about1,000 rpm to about 2,000 rpm) for a time period of from about 10 secondsto about 120 seconds (preferably from about 30 seconds to about 90seconds). After the composition is applied, it is preferably heated to atemperature from about 60° C. to about 350° C., and more preferably fromabout 140° C. to about 250° C. and for time periods from about 30seconds to about 20 minutes, preferably from about 1 minutes to about 15minutes. The release layer 32 is then subjected to a high-temperaturefinal bake at a temperature of from about 250° C. to about 350° C., andmore preferably from about 280° C. to about 320° C., and preferably fortime periods of from about 2 minutes to about 60 minutes, morepreferably about 10 minutes.

In one embodiment, this final bake pushes the polymerization reaction tocompletion by causing a chain extending reaction to take place among twoor more of the polyketanil chains present in the laser release layer 32.Thus, in these instances, the polyketanil chains present after heatinghave a higher molecular weight than the chains present before heating.In embodiments where a crosslinking agent is included, one or bothheating stages will cause crosslinking to take place, thus resulting ina crosslinked polyketanil in the release layer 32.

In some embodiments, it is preferable to subject the release layer 32 toa multi-stage bake process, depending upon the composition utilized.Also, in some instances, the above application and bake process can berepeated on a further aliquot of the composition, so that the laserrelease layer is “built” on the second substrate in multiple steps.

Regardless of the embodiment, after heating, release layer 32 preferablyhas an average thickness of from about 10 nm to about 5,000 nm, morepreferably from about 100 nm to about 1,000 nm, and even more preferablyfrom about 150 nm to about 750 nm. Thicknesses as used herein can bemeasured using any film thickness measurement tool, with one preferredtool being an infrared interferometer, such as those sold by SUSSMicrotec or Foothill.

In a further embodiment, a polyketanil composition according to theinvention can be formed into a preformed, dry film rather than appliedas a flowable composition. In this instance, the composition is formedinto an unsupported, self-sustaining film that doesn't collapse orchange shape (absent application of force or energy) even though it isunsupported. This film can then be adhered to the second substrate toform the release layer 32.

The laser release layer 32 will have a k value at the desired wavelength(i.e., the wavelength for debonding or decomposing the bonding layer 20)of at least about 0.1, preferably at least about 0.2, more preferably atleast about 0.24, and even more preferably from about 0.24 to about 0.5.The n value of the laser release layer 32 will at least about 1.4,preferably at least about 1.5, more preferably at least about 1.6, andeven more preferably from about 1.7 to about 2.

Referring to structure 22 of FIG. 1(a) again, although release layer 32is shown to cover the entire surface 26 of second substrate 24, it willbe appreciated that it could be present on only portions or “zones” ofcarrier surface 26 similar to as was described with bonding layer 20.

Structures 10 and 22 are then pressed together in a face-to-facerelationship, so that upper surface 21 of bonding layer 20 is in contactwith upper surface 33 of release layer 32 (FIG. 1(b)). While pressing,sufficient pressure and heat are applied for a sufficient amount of timeso as to effect bonding of the two structures 10 and 22 together to formbonded stack 34. The bonding parameters will vary depending upon thecomposition from which bonding layer 20 is formed, but typicaltemperatures during this step will range from about 25° C. to about 250°C., and preferably from about 150° C. to about 220° C., with typicalpressures ranging from about 1,000 N to about 25,000 N, and preferablyfrom about 3,000 N to about 10,000 N, for a time period of from about 30seconds to about 20 minutes, and preferably from about 3 minutes toabout 10 minutes.

In an alternative embodiment, it will be appreciated that bonding layer20 could be applied to upper surface 33 of release layer 32, using theapplication process described previously, rather than being applied tosurface 14 of first substrate 12. In this instance, the first substrate12 would then be subjected to the above bonding process so as to bondsurface 14 of first substrate 12 to bonding layer 20, which waspreviously formed on upper surface 33 of release layer 32.

The bonded stack should have a TTV of less than about 10% of the totalaverage thickness, preferably less than about 5% of the total averagethickness (measured at five locations across the stack), and even morepreferably less than about 3% of the total average thickness of thebonded stack. That is, if the bonded stack has an average thickness of100 μm, TTV of less than about 10% would be about 10 μm or lower.

Regardless of which embodiment was used to form the bonded stack 34, thefirst substrate 12 can now be safely handled and subjected to furtherprocessing that might otherwise have damaged first substrate 12 withoutbeing bonded to second substrate 24. Thus, the structure can safely besubjected to backside processing such as back-grinding,chemical-mechanical polishing (“CMP”), etching, metal deposition (i.e.,metallization), dielectric deposition, patterning (e.g.,photolithography, via etching), passivation, annealing, and combinationsthereof, without separation of substrates 12 and 24 occurring, andwithout infiltration of any chemistries encountered during thesesubsequent processing steps. Not only can bonding layer 20 and releaselayer 32 survive these processes, they can also survive processingtemperatures up to about 300° C., preferably from about 150° C. to 280°C., and more preferably from about 180° C. to about 250° C. for at leastabout 60 minutes, and preferably from about 90 minutes to about 15hours.

Once processing is complete, the substrates 12 and 24 can be separatedby using a laser to decompose or ablate all or part of the laser releaselayer 32. Suitable laser wavelengths include those of from about 200 nmto about 400 nm, and preferably from about 300 nm to about 360 nm. Inorder to debond the laser release layer 32, a laser is scanned acrossthe surface of the substrate 24 in a stand-and-repeat method or linescan method in order to expose the entire wafer. Exemplary laserdebonding tools include the SUSS MicroTec Lambda STEEL 2000 laserdebonder and Kingyoup laser debonder. The substrate 24 is preferablyscanned by the laser spot with a field size from about 40×40 m to about12.5×4 mm. Suitable fluence to debond the substrates 12, 24 is fromabout 100 mJ/cm² to about 400 mJ/cm², and preferably from about 150mJ/cm² to about 350 mJ/cm². Suitable power to debond the substrates 12,24 is from about 0.5 W to about 6 W, and preferably from about 1 W toabout 2 W.

After laser exposure, the substrates 12 and 24 will readily separate.After separation, any remaining bonding layer 20 can be removed with aplasma etch or a solvent capable of dissolving the bonding layer 20.

For the plasma cleaning, O₂ plasma may be used alone, or a combinationof O₂ plasma and fluorinated gas in a ratio of from about 1:1 to about10:1 may be used, at a power of 100 W and higher.

Solvent cleaning can be performed by bath or spin cleaning process.Suitable solvents include for nonpolar bonding materials include, butare not limited to, d-limonene, mesitylene, 1-dodecene, and combinationsthereof. Suitable solvents for cleaning polar bonding materials includeGBL, cyclopentanone, benzyl alcohol, DMSO, cyclohexanone, PGME, PGMEA,NMP, 1,3-dioxolane, and combinations thereof.

When a spin cleaning process is used, it is preferably performed forabout 1 minute to about 15 minutes of clean time. In the spin cleaningprocess, solvent is sprayed in the center of the wafer with acombination of puddle and soak cycle and then is spun off. For a puddleand soak cycle, solvent is sprayed in the center of the wafer andpuddled out at a spin speed of from about 20 rpm to about 150 rpm and issoaked with no solvent spraying or rotation of the wafer for about 30seconds to about 90 seconds. In the final step, solvent is dispensed inthe center of the substrate, and the substrate is spun at a spin speedof from about 750 rpm to about 1,500 rpm.

In the above embodiments, the release layer 32 is shown on a secondsubstrate 24 that is a carrier wafer, while bonding layer 20 is shown ona first substrate 12 that is a device wafer. It will be appreciated thatthis substrate/layer scheme could be reversed. That is, the releaselayer 32 could be formed on first substrate 12 (the device wafer) whilebonding layer 20 is formed on second substrate 24 (the carrier wafer).The same compositions and processing conditions would apply to thisembodiment as those described above, except that bonding layer 20 wouldbe selected so that laser energy could pass through it, after passingthrough second substrate 24, thus allowing the laser energy to makecontact with release layer 32.

Additionally, it will be appreciated that bonding layer 20 and releaselayer 32 could be used with or as additional bonding materials,structural support layers, lamination aid layers, tie layers (foradhesion to initial substrate), contamination control layers, andcleaning layers. Preferred structures and application techniques will bedictated by application and process flow.

2. Build-Up Layer Embodiment

In a further embodiment, the polyketanil compositions described hereincan be used as a build-up layer for redistribution layer (“RDL”)formation, and particularly in RDL-first/chip-last packaging in wafer-or panel-level processes, which is good for minimizing or even avoidingknown-good die loss during packaging. A schematic of one such process isshown in FIG. 2 .

A polyketanil composition as described previously is applied to theupper surface 38 of a carrier substrate 40 to form a laser-releasablebuild-up layer 42 on the carrier surface 38, as shown in FIG. 2(a).Build-up layer 42 is formed following any of the methods described withrespect to the temporary bonding embodiment above, including theprocessing conditions and resulting properties. Build-up layer 42 has anupper surface 44 remote from carrier substrate 40, and preferably thebuild-up layer 42 is formed directly on the upper surface 38 of carriersubstrate 40 (i.e., without any intermediate layers between the build-uplayer 42 and substrate 40).

Next, a seed layer 46 is deposited on upper surface 44 followingconventional methods (FIG. 2(b)). The seed layer 46 can then be coatedwith a photoresist, patterned, and electroplated, again following knownmethods, forming the structure shown in FIG. 2(c). Referring to FIG.2(d), the photoresist is stripped, and the metal etched, followed bycoating, patterning, and curing of a dielectric layer. This results inthe formation of the first RDL 48, as shown in FIG. 2(e). The steps ofFIG. 2(b) to FIG. 2(e) can be repeated multiple times, as needed, tocreate multiple RDLs (48(a)-(d), i.e., four RDLs, in the embodimentshown in FIG. 2(f)).

Referring to FIG. 2(g), after the desired number of RDLs have beenformed, solder balls 50 are attached to the uppermost (last formed) RDL,again following conventional methods. A die 52 is bonded to solder balls50, followed by application and grinding of a conventional epoxy moldinglayer 54, forming a fan-out wafer level package structure 56. Finally,laser energy is applied to the carrier substrate 40, followingpreviously described laser separation conditions, so as to decompose orablate all or part of the laser-releasable build-up layer 42. Afterlaser application, the carrier substrate 40 will be released andseparated from fan-out wafer level package structure 56 (FIG. 2(h)),with any remaining build-up layer 42 being removed by a solvent.

It should be noted that the above-described process for forming fan-outwafer level package structures is only one example of this type ofprocess that can be carried out using the inventive composition as abuild-up layer, and that variations of this process can and will bemade, depending upon user needs. For example, the number of RDL layerscan be varied, as needed, as well as the number and positioning ofsolder balls and dies. These arrangements will be understood andcustomized by one skilled in this art.

As can be seen above, the present invention offers many advantages. Thepolyketanils (and thus layers formed therefrom) offer high absorbancesat a wide variety of wavelengths, including those primarily used forlaser debond (about 300 nm to about 400 nm) to all the way up to thevisible range of light. Additionally, the high absorbances of thepolyketanils allow for casting of thinner films on the wafer while stillabsorbing most to all of the laser energy to prevent device damage. Thehigh absorbances also offer benefits to reducing the laser energy andtime required to debond the wafers. And along with the direct benefitsto laser debonding, these materials can also be used in RDL-firstprocesses. The polymers can utilize various monomers, allowing thestructures to become insoluble by crosslinkable groups or chainextension. This class of polymers can provide thermal stability of 300°C. or greater, provide good adhesion to silicon as well as glasssubstrates, and can be removed by dry-etch (plasma etching) with similaretch rates as polyimides. Finally, due to the thinner films required,stress and bow can be reduced on both silicon and glass substrates.

Additional advantages of the various embodiments will be apparent tothose skilled in the art upon review of the disclosure herein and theworking examples below. It will be appreciated that the variousembodiments described herein are not necessarily mutually exclusiveunless otherwise indicated herein. For example, a feature described ordepicted in one embodiment may also be included in other embodiments butis not necessarily included. Thus, the present invention encompasses avariety of combinations and/or integrations of the specific embodimentsdescribed herein.

“Polyketanil” when included in a composition or a layer above isintended to include a single type of polyketanil as well as two or moredifferent types of polyketanils, unless stated otherwise. Additionally,as used herein, the phrase “and/or,” when used in a list of two or moreitems, means that any one of the listed items can be employed by itselfor any combination of two or more of the listed items can be employed.For example, if a composition is described as containing or excludingcomponents A, B, and/or C, the composition can contain or exclude Aalone; B alone; C alone; A and B in combination; A and C in combination;B and C in combination; or A, B, and C in combination.

The present description also uses numerical ranges to quantify certainparameters relating to various embodiments of the invention. It shouldbe understood that when numerical ranges are provided, such ranges areto be construed as providing literal support for claim limitations thatonly recite the lower value of the range as well as claim limitationsthat only recite the upper value of the range. For example, a disclosednumerical range of about 10 to about 100 provides literal support for aclaim reciting “greater than about 10” (with no upper bounds) and aclaim reciting “less than about 100” (with no lower bounds).

EXAMPLES

The following examples set forth methods in accordance with theinvention. It is to be understood, however, that these examples areprovided by way of illustration and nothing therein should be taken as alimitation upon the overall scope of the invention.

Example 1 Polymerization to Form Polyketanil

In this procedure, 13.07 grams of 4′-aminoacetophenone (Alfa Aesar,Haverhill, Mass.) were dissolved in 20.76 grams of gamma butyrolactone(GBL, Sigma Aldrich, St. Louis, Mo.) in a four-necked 1-literround-bottom flask. The flask was equipped with a heating mantle,temperature controller, thermal probe, Dean-Stark trap and overheadstirrer with stir bar and paddle mixer. A condenser was attached to theDean-Stark trap. Nitrogen flow was initiated to the flask, and thereaction was heated to 110° C. Next, 0.06 grams (0.18%) of 96% sulfuricacid (KMG Chemicals, Ft. Worth, Tex.) was added to the solution, andthen the solution was heated to 185° C. The water and GBL mixture wascollected in the Dean-Stark trap (˜7% of the total solution weight) andwas not added back into the system. The solution was allowed to reactfor 48 hours and then was cooled to room temperature. The resultingsolution was approximately 35% solids, and was a dark red, slightlyviscous solution. The cooled solution was then bottled for further use.

Example 2 Preparation of Polyketanil Composition

In the Example, 634.20 grams of the solution from Example 1 was mixedwith 665.86 grams of ethyl lactate (KMG Chemicals, Ft. Worth, Tex.) byan overhead stir motor. The mixture was stirred until all solids were insolution. The resulting solution was then filtered using a 0.2-μmMeissner filter.

Example 3 Characterization of Polyketanil Composition 1. OpticalProperties

The material prepared in Example 2 was coated on a 100-mm Si wafer. Thiscoating was accomplished by spin coating at 1,500 rpm with anacceleration of 1,500 rpm/s for 60 seconds. The carrier wafer was thenbaked at 150° C. for 2 minutes, 220° C. for 2 minutes, 250° C. for 5minutes, and 300° C. for 10 minutes. The coated wafer was then run on aVASE M2000 ellipsometer to obtain raw optical data. The data was thenfit for thickness and optical properties (n & k values). The wavelengthsof interest were 308 nm, 343 nm, and 355 nm. The results are summarizedin Table 1, and the full spectrum is shown in FIG. 3 .

TABLE 1 Optical constants Wavelength (nm) n k 308 1.84 0.43 343 1.870.26 355 1.86 0.24

2. Thickness, Molecular Weight, and Polydispersity Index

The material prepared in Example 2 was coated on a 200-mm glass wafer.This coating was accomplished by spin coating at 1,500 rpm with anacceleration of 1,500 rpm/s for 60 seconds. The carrier wafer was thenbaked at 150° C. for 2 minutes, 220° C. for 2 minutes, 250° C. for 5minutes, and 300° C. for 10 minutes. The coated wafer was then analyzedon an FRT Microprof® 300 tool using a 1×1 mm resolution point map scan,resulting in an average thickness value of 673.48 nm and a TTV of 32.89nm with a 1% high and low data exclusion.

GPC was performed with a Waters 717 liquid chromatography system usingNMP, THF, acetic acid, and lithium bromide and a mobile phase flow of 1ml/min. Detection was accomplished with a Waters 410 differentialrefractive index detector, and the signal was integrated and quantitatedusing relative calibration with polystyrene standards. Table 2 showsthese results.

TABLE 2 Average Molecular Weight and Poly dispersity Index (“PDI”) Mw(Daltons) Mn (Daltons) Mz (Daltons) PDI 2809 1623 4682 1.73

Example 4 Bonding Using Formulation of Example 2

The material prepared in Example 2 was coated on a 200-mm glass wafer asa carrier wafer. This coating was accomplished by spin coating at 1,500rpm with an acceleration of 1,500 rpm/s for 60 seconds. The carrierwafer was then baked at 60° C. for 2 minutes, 120° C. for 2 minutes,250° C. for 5 minutes, and 300° C. for 10 minutes. An experimentalphenoxy-based thermoplastic bonding material (Brewer Science, Rolla,Mo.) was coated on a 200-mm silicon wafer as a simulated device wafer.This coating was accomplished by spin coating at 1,500 rpm with anacceleration of 3,000 rpm/s for 30 seconds. The carrier wafer was thenbaked at 60° C. for 5 minutes, 160° C. for 5 minutes, and 220° C. for 5minutes. The coated carrier wafer was bonded to the coated device waferby bonding at 200° C., 3000 N for 3 minutes under vacuum (<5 mbar) in anEVG®510 bonding system (EV Group).

Example 5 Laser Debonding and Cleaning Using Formulation of Example 2

The bonded wafer pairs were successfully debonded by using the threemajor UV-laser wavelengths currently used by the industry. A differentpiece of debonding equipment was used for each wavelength, and thatequipment was: a SUSS ELD12 Laser Debonder (Garching bei Munchen,Germany); an EVG Semi-Automatic Debonding System (St. Florian/Inn,Austria); and a Kingyoup LD-Semi Automatic 200/300 (New Taipei City,Taiwan). The laser debonding parameters and results from the SUSS,Kingyoup, and EVG debonders are shown in Tables 3, 4, and 5,respectively.

TABLE 3 Laser Debonding Parameters and Results for SUSS Debonder FLUENCERESULTS (mJ/cm²) (beam size of 12.5 × 4 mm and overlap of 100-200 μm)160 Debonded Successfully; low residue observed 200 DebondedSuccessfully; higher residue observed

TABLE 4 Results from Kingyoup Debonder POWER SCAN LINE PITCH SCAN RESULT(W) SPEED (m/s) (um) TIME (s) (beam size of 60 μm) 2 3.5 70 128.2Debonded Successfully 1.5 3.4 69 133.9 Debonded Successfully 1.2 2.6 53228.0 Debonded Successfully

TABLE 5 Results from EVG Debonder FLUENCE RESULT (mJ/cm²) (beam size of40 × 40 μm and pitch size of 40 μm) 750 Debonded successfully; showedvery low carbon residue 500 Debonded successfully; showed no carbonresidue and no transmittance through UV tape

Example 6 Blending of Polyketanil with Low Absorbing Material

The procedure was carried out to show how the inventive polymers andcompositions can be blended with other polymer compositions to improvethe properties of those polymer compositions. In this instance, theother polymer composition included a 12% weight solution of acommercially available polyimide, which is low absorbing at 300-400 nm,in a GBL-cyclopentanone solvent mixture (referred to as “PolyimideSolution”).

A 17.5% by weight solution of the material prepared Example 1 was mixedwith cyclopentanone (obtained from FujiFilm) in a 1:1 weight ratio(referred to as “Polyketanil Additive”). The Polyketanil Additive wasmixed with the Polyimide Solution at different ratios, with the weightsof each being summarized in Table 6.

TABLE 6 Weights of Polyketanil Additive and Polyimide Solution BlendedWT. OF POLYKETANIL WT. OF POLYIMIDE ADDITIVE ADDITIVE (g) SOLUTION (g)PERCENT* 1.03 5.14 16.7% 2.08 5.07 29.1% 3.02 5.02 37.5% 4.03 5.1643.8% *$\left\lbrack \frac{{{Wt}.{of}}{Polyketanil}{Additive}}{\left( {{{{Wt}.{of}}{Polyketanil}{Additive}} + {{{Wt}.{of}}{Polyimide}{Solution}}} \right.} \right\rbrack \times 100$

The prepared solutions were spin coated to obtain films thin enough tomeasure the absorbance (k) ranging from A thickness of 100 nm to 500 nm.This coating was accomplished by spin coating at 1,500 rpm with anacceleration of 1,500 rpm/s for 60 seconds. The wafers were baked at 60°C. for 2 minutes, 150° C. for 2 minutes, and 220° C. for 5 minutes. Thecoated wafer was then run on a VASE M2000 ellipsometer to obtain rawoptical data. The data was then fit for thickness and optical properties(n & k values). The wavelengths of interest were 308 nm, 343 nm, and 355nm. These results are summarized in Table 7.

TABLE 7 Change of k Values at Major Wavelengths with DifferentPercentage of Polyketanil Additive POLYKETANIL k VALUE k VALUE k VALUEADDITIVE % AT 308 NM AT 343 nm AT 355 nm  0.00% 0.08 0.03 0.03 43.84%0.27 0.15 0.14 37.51% 0.21 0.13 0.12 29.13% 0.19 0.11 0.10 16.72% 0.140.07 0.07

We claim:
 1. A polymer comprising recurring monomers of

where each of R₁ to R₄: can be the same or different; and isindividually selected from the group consisting of hydrogen, alkyls,alkoxys, hydroxyls, and polyethylene glycol chains.
 2. The polymer ofclaim 1, wherein each R is hydrogen.
 3. The polymer of claim 1, whereinsaid polymer has a weight average molecular weight of from about 1,000Daltons to about 100,000 Daltons.